The prior art is replete with the use of edible tubular casings for sausage meat wherein the casing is made of certain intestines of animals. Such casings are not completely satisfactory as they are relatively scarce. As they are retrieved during conventional animal butchering steps the casings are often inadvertently marred by knife nicking during the butchering process making such intestines useless as casing material. In addition the thickness of the wall and diameter of these casings will vary, causing difficulty during modern high speed stuffing.
As a result of the difficulties and increased expense associated with intestine derived casings, also know as natural casings, the industry has experimented and disclosed the use of both artificial edible casings and artificial non-edible casings. The latter, of course, have the decided disadvantage in that the artificial non-edible casings have to be removed from the meat product prior to use.
The artificial edible casings are conventionally fabricated from a composition incorporating large quantities of collagen. The latter is also available from by-products in butchering processes. Collagen, while very useful, is only available on a limited scale and is therefor relatively expensive.
As stated, traditionally, artificial, edible-type sausage casings have been prepared from animal derived collagen e.g. U.S. Pat. No. 3,123,653 Lieberman, E. R. and U.S. Pat. No. 3,525,628 Cohly, M. A. Specifically, edible casings have been prepared by processing animal hides in such a way as to disrupt the collagen structure into an extrudable mass which is reformed into a tubular membrane. The process is very complex and involves many time consuming steps to chemically and mechanically treat the collagen material. Because this natural protein is very heat sensitive, the process must be carried out under conditions of low temperature to avoid undesirable degradation. Thus, traditional "hot melt" extrusion techniques which are commonly used in producing conventional plastic packaging materials is not appropriate. Additionally, since collagen materials must be extruded at relatively low solids concentrations (3.5 to 8.0%), both chemical dewatering and forced air drying are used to obtain a suitable product for use in sausage products.
Gelatin has been considered for use in preparing edible packaging materials because it is more economical to obtain than is collagen and because it can be sourced as a dry powder which is easily handled and stored. Although gelatin has been successfully used at low concentration as an additive to improve or modify the properties of collagen casings, there has not been a successful method for producing a predominately gelatin casing.
Lieberman in U.S. Pat. No. 3,346,402 describes a method of extruding a homogeneous mixture of 80 to 95 parts of swollen tendon collagen and 5 to 20 parts of gelatin to form a continuous tube for use as a sausage casing. The extruded tube must be coagulated, tanned, plasticized, and dried to obtain a moisture content of 10-30%. If more than 20% gelatin is present, the extruded tubing lacks sufficient strength to function as a casing.
European Patent 0,038,628 to Kosugi, J. et al discloses a method for producing a modified composite structure by partially replacing collagen with gelatin. Levels of approximately 5% gelatin were used. The material was not suitable for extrusion into a tube, but rather was formed into a casing by using an electrodeposition process. This method does not lend itself to high speed production methods.
U.S. Pat. No. 3,943,262 to Winkler, B. et al utilizes small amounts of gelatin as the carrier and fixative for dyes that are added to edible collagen casings. U.S. Pat. No. 3,917,862 to Bridgeford, D. J. employs gelatin as an adhesive used for patching edible artificial sausage casings. Gelatin has also been used as a coating on the inside of non-edible fibrous casings to improve adhesion of the casing to the surface of dried sausage, e.g. German Offen. 2,100,210, O'Brien, M. N. et al and U.S. Pat. No. 3,383,223, Rose H. J.
Under normal conditions it is exceedingly difficult to produce tubular sausage casings from gelatin. Because of viscosity effects and difficulties in mixing uniform solutions, gelatin concentrations are normally used at relatively low concentrations typically 5 to 15% and rarely above 25%. Extrusion of this material is usually carried out under low pressure and the resulting film layer must be supported on a coating surface such as a release belt or casting drum. These films are too weak to be self supporting in either sheet or tubular form. Also, because of the moisture contents, the material must be passed through a drying chamber to increase the solid conentration.
A number of other edible compositions have been contemplated in the fabrication of edible tubular casings for meat, but have not met with success. Usually, such other products have been unduely expensive but more importantly have not provided the appropriately needed strength and physical properties necessary to sustain the encased meat product during its shelf life period in a refrigerated case in a store or home. More, importantly, the casing may not withstand the rigors accompanying the cooking process.